The present invention relates to an exhaust support system for use in a midship engine rear wheel drive-type vehicle, and more particularly to an exhaust support system located between a catalytic converter and a muffler.
In general, a midship engine rear wheel drive-type vehicle, as shown in FIG. 1, has an engine 3 located between a rear axle shaft 1 and a passenger seat 2. In such a vehicle, a nearly equivalent load is exerted on a front axle shaft 4 and the rear axle shaft 1. Hence, the steering control of this vehicle is superior to the steering control of other types of vehicles, resulting in midship engines being installed in many sports cars. To further improve the performance of the steering control in sports cars equipped with midship engines, the lengths l.sub.1 and l.sub.2 of a front overhang and a rear overhang 5 and 6, respectively, as shown in FIG. 1, are designed to be as short as possible. These short overhangs make it difficult to locate a muffler 7 parallel to the longitudinal direction of the vehicle under the overhang 6 because of the limited size of the rear overhang 6. Hence, in the midship engine rear wheel drive-type sports car of FIG. 10, the muffler 7 is positioned laterally across the vehicle. The reference FWD in FIG. 10 designates a forward direction in the vehicle.
Further, in general, engine vibrations are transmitted through an exhaust pipe to a muffler. If such vibrations are transmitted from the muffler to the vehicle body, the vehicle body vibrates and undesirable noise results in the passenger compartment. This impairs the passenger's comfort. Hence, to absorb the vibration of a muffler, the muffler is mounted through a resilient member onto the body of the vehicle.
In a midship engine rear wheel drive-type vehicle, as shown in FIG. 1, the engine 3 is mounted at a position between the rear axle shaft 1 and the passenger seat 2. The engine 3 is transversely mounted, as shown in FIG. 10, because of the limited longitudinal length of the rear overhang 6. In a vehicle having a transversely mounted engine, a muffler has been mounted onto the vehicle body through a resilient member which is flexible upwardly and downwardly, with a small amount of force. FIG. 10 shows resilient members 12 and 13, which are in the form of disc plates. The members 12 and 13 are located on the same horizontal plane. One end of the members 12 and 13 is fixed to longitudinal ends 10 and 11 of the muffler 7, respectively. A second end of each of the members 12 and 13 is fixed to side members 18 and 19, respectively. The resilient members 12 and 13 are relatively thin in the direction in which they are upwardly and downwardly flexible and therefore bend quite easily in this direction (the upward and downward displacement corresponds to the arrows V--V in FIG. 11).
When the engine 3 is running, it rolls about the axial line N--N of a crank shaft (not shown in drawings) in the direction designated by an arrow C in FIG. 10. In a vehicle having a longitudinally mounted engine, as shown in FIG. 6, the distance "l" between the axial line N--N of the crank shaft and an exhaust pipe 8 is small. While in a vehicle having a transversely mounted engine, as shown in FIG. 7, the distance "L" between the axial line N--N of the crank shaft and a tail end of the exhaust pipe 8 is large. Hence, in the vehicle having a transversely mounted engine, the exhaust pipe 8 amplifies the amplitude of the vibration of the engine roll (the vibration in the direction of the arrows C--C about the axial line N--N in FIG. 7). The amplified engine roll causes the muffler 7 to vibrate upwardly and downwardly with great amplitude. To attenuate this upward and downward vibration of the muffler 7, resilient members similar to the resilient members 12 and 13 have been utilized.
In a vehicle having a transversely mounted engine, the reduction of vibrations in the muffler 7 is accomplished by a vibration absorbing device 9, as shown in FIG. 10. The vibration absorbing device 9 is provided on the exhaust pipe 8, which connects an exhaust manifold of the engine 3 with the muffler 7. The vibration absorbing device 9 absorbs the vibration of the engine 3 and is designed such that it does not transmit the vibration of the engine 3 into the muffler 7. For example, a ball joint can be included in the vibration absorbing device 9. The numeral 14 designates a catalytic converter which purifies the exhaust gas therein. The vibration absorbing device 9 cannot completely absorb the vibration of the engine 3. Hence, the resilient members 12 and 13 are designed to bend upwardly and downwardly with small amounts of force, compared with resilient members in a vehicle having a longitudinally mounted engine.
When a vehicle vibrates because of rough road conditions, the resilient members 12 and 13 will readily bend in an upwardly and downwardly manner (the direction of the arrows V--V in FIG. 9), whenever the muffler 7 and the catalytic converter 14 are displaced upwardly and downwardly because of rough road conditions. The muffler 7 and the catalytic converter 14 individually and collectively have a considerable weight. Hence, the amplitude of the upward and downward vibrations can be considerable. Further, the muffler 7 and the catalytic converter 14 do not always vibrate upwardly and downwardly in phase with each other. Specifically, when the muffler is upwardly displaced, the catalytic converter may be downwardly displaced. When the vehicle is caused to vibrate upwardly and downwardly because of rough road conditions, the engine 3 also vibrates upwardly and downwardly. However, the engine 3 might also vibrate out of phase with the muffler 7 and the catalytic converter 14. Hence, a large relative vertical displacement is possible between the muffler 7, the catalytic coverter 14 and the engine 3. The catalytic converter 14 is located under the muffler 7, as shown in FIG. 11. The axial line M--M of the catalytic converter 14 is provided to be parallel to the axial line L--L of the muffler 7. This layout is determined by the limited size of the vehicle. Further, the catalytic converter 14 and the muffler 7 are directly connected by a U-shaped exhaust pipe 25.
The catalytic converter 14 and the engine 3 is connected by the exhaust pipe 8, upon which the vibration absorbing device 9 is provided. Hence, even if a relative displacement is generated between the catalytic converter 14 and the engine 3, such a displacement is absorbed by the vibration absorbing device 9. This permits the exhaust pipe 8 to escape any damage due to such a displacement. However, if the relative displacement is generated between the catalytic converter 14 and the muffler 7, the exhaust pipe 25 might be subjected to some damage because the catalytic converter 14 and the muffler 7 are connected directly by the exhaust pipe 25.
Hence, according to known techniques, the catalytic converter 14 is mounted through a bracket 26 onto the muffler 7, to prevent a relative displacement between the catalytic converter 14 and the muffler 7 when the assembly is subjected to upward and downward vibrations.
Further, when the temperature increases within the muffler 7 and the catalytic converter 14, the muffler 7 and the catalytic converter 14 expand along their longitudinal directions. During operation of the engine 3, the temperature of the muffler 7 is lower than that of the catalytic converter 14. Hence, the amount of the thermal expansion between the muffler 7 and the catalytic converter 14 will be different. Unless the muffler 7 and the catalytic converter 14 are designed to be slidable with respect to each other, in their longitudinal directions, the exhaust pipe 25 could be damaged.
To avoid the damage of the exhaust pipe 25, the bracket 26, which mounts the catalytic converter 14 onto the muffler 7, is designed to be a thin sheet which extends perpendicular to the axial lines L--L of the muffler 7 and M--M of the catalytic converter 14. This design permits the bracket 26 to bend easily along the axial line M--M thereof, but the bracket 26 cannot easily bend upwardly and downwardly. According to such a design, the damage of the exhaust pipe 25 is prevented even when differential thermal expansion between the muffler 7 and the catalytic converter 14 exists, as well as any upward and downward vibrations.
However, according to the design shown in FIGS. 10 and 11, the following disadvantages are present.
As shown in FIG. 11, the catalytic converter 14 is provided underneath the muffler 7, and further, the bracket 26 extends downwardly. The bracket 26 is made of a sheet of metal. Hence, when the bracket 26 is subjected to a sufficient upward force, the bracket 26 will buckle. If the bracket 26 buckles, the catalytic converter 14 is displaced to a position which is closer to the muffler 7. As a result of this relative displacement, the exhaust pipe 25 might be damaged. Further, the bracket 26 is bent into a L-shaped form and is fixed by a bolt 56 and a nut 57 to the muffler 7. Hence, when the bracket 26 is subjected to a downward force, the portion between the bolt 56 and a bend portion 58 of the L-shaped bracket 26, constitutes a cantilever. Thus, the downward force is amplified due to the cantilever action and the L-shaped bracket 26 readily bends. If the L-shaped bracket 26 downwardly bends, the catalytic converter 14 is downwardly displaced relative to the muffler 7, which also can result in damage to the exhaust pipe 25.
To avoid the above-described disadvantages, one solution to prevent relative displacement between the muffler 7 and the catalytic converter 14 is to increase the thickness of the bracket 26. However, when the thickness of the bracket 26 is increased, the stiffness of the bracket 26 is enhanced in the axial direction M--M thereof. This increased stiffness prevents the relative displacement between the muffler 7 and the catalytic converter 14, generated by the relative thermal expansion differences. Hence, the thickness of the bracket 26 is limited because of the need to compensate for differential thermal expansion between the muffler 7 and the catalytic converter 14.
Another solution to avoid the above-described disadvantages is to provide another vibration absorbing device on the exhaust pipe 25 to absorb the relative displacement between the catalytic converter 14 and the muffler 7. However, according to this solution, two vibration absorbing devices are needed on the exhaust pipes 8 and 25, respectively. This results in an increased production cost.